Platelet factor 4 (PF-4)-induced neutrophil adhesion is controlled by src-kinases, whereas PF-4-mediated exocytosis requires the additional activation of p38 MAP kinase and phosphatidylinositol 3-kinase

Dissecting thrombus-directed chemotaxis and random movement in neutrophil near-thrombus motion in flow chambers

BACKGROUND

Thromboinflammation is caused by mutual activation of platelets and neutrophils. The site of thromboinflammation is determined by chemoattracting agents release by endothelium, immune cells, and platelets. Impaired neutrophil chemotaxis contributes to the pathogenesis of Shwachman-Diamond syndrome (SDS). In this hereditary disorder, neutrophils are known to have aberrant chemoattractant-induced F-actin properties. Here, we aim to determine whether neutrophil chemotaxis could be analyzed using our previously developed ex vivo assay of the neutrophils crawling among the growing thrombi.

METHODS

Adult and pediatric healthy donors, alongside with pediatric patients with SDS, were recruited for the study. Thrombus formation and granulocyte movement in hirudinated whole blood were visualized by fluorescent microscopy in fibrillar collagen-coated parallel-plate flow chambers. Alternatively, fibrinogen, fibronectin, vWF, or single tumor cells immobilized on coverslips were used. A computational model of chemokine distribution in flow chamber with a virtual neutrophil moving in it was used to analyze the observed data.

RESULTS

The movement of healthy donor neutrophils predominantly occurred in the direction and vicinity of thrombi grown on collagen or around tumor cells. For SDS patients or on coatings other than collagen, the movement was characterized by randomness and significantly reduced velocities. Increase in wall shear rates to 300-500 1/s led to an increase in the proportion of rolling neutrophils. A stochastic algorithm simulating leucocyte chemotaxis movement in the calculated chemoattractant field could reproduce the experimental trajectories of moving neutrophils for 72% of cells.

CONCLUSIONS

In samples from healthy donors, but not SDS patients, neutrophils move in the direction of large, chemoattractant-releasing platelet thrombi growing on collagen.

Platelet Physiology

Platelets are the smallest blood cells, numbering 150 to 350 × 109/L in healthy individuals. The ability of activated platelets to adhere to an injured vessel wall and form aggregates was first described in the 19th century. Besides their long-established roles in thrombosis and hemostasis, platelets are increasingly recognized as pivotal players in numerous other pathophysiological processes including inflammation and atherogenesis, antimicrobial host defense, and tumor growth and metastasis. Consequently, profound knowledge of platelet structure and function is becoming more important in research and in many fields of modern medicine. This review provides an overview of platelet physiology focusing particularly on the structure, granules, surface glycoproteins, and activation pathways of platelets.

Luteolin peracetate and gossypolone inhibit immune complex-mediated neutrophil activation in vitro and dermal-epidermal separation in an ex vivo model of epidermolysis bullosa acquisita

Introduction

Natural products have been shown to an important source of therapeutics for human disease. In this study, we aimed to identify natural compounds as potential therapeutics for epidermolysis bullosa acquisita (EBA), an autoimmune disease caused by autoantibodies to type VII collagen (COL7).

Methods

Utilizing an in vitro experimental system, we screened a natural product library composed of 800 pure compounds for their inhibitory effect on COL7-anti-COL7 IgG immune complex (IC)-mediated neutrophil activation and on neutrophil-mediated tissue damage.

Results

Three natural compounds, namely luteolin peracetate, gossypol, and gossypolone were capable in inhibiting the IC-induced neutrophil adhesion and oxygen burst in vitro. Furthermore, luteolin peracetate and gossypolone were able to inhibit the anti-COL7 IgG induced dermal-epidermal separation in an ex vivo model for EBA.

Discussion

In summary, this study demonstrates that luteolin peracetate and gossypolone are potential therapeutics for experimental EBA, which deserves further investigation.

Chemokine Heteromers and Their Impact on Cellular Function-A Conceptual Framework

Chemoattractant cytokines or chemokines are proteins involved in numerous biological activities. Their essential role consists of the formation of gradient and (immune) cell recruitment. Chemokine biology and its related signaling system is more complex than simple ligand-receptor interactions. Beside interactions with their cognate and/or atypical chemokine receptors, and glycosaminoglycans (GAGs), chemokines form complexes with themselves as homo-oligomers, heteromers and also with other soluble effector proteins, including the atypical chemokine MIF, carbohydrate-binding proteins (galectins), damage-associated molecular patterns (DAMPs) or with chemokine-binding proteins such as evasins. Likewise, nucleic acids have been described as binding targets for the tetrameric form of CXCL4. The dynamic balance between monomeric and dimeric structures, as well as interactions with GAGs, modulate the concentrations of free chemokines available along with the nature of the gradient. Dimerization of chemokines changes the canonical monomeric fold into two main dimeric structures, namely CC- and CXC-type dimers. Recent studies highlighted that chemokine dimer formation is a frequent event that could occur under pathophysiological conditions. The structural changes dictated by chemokine dimerization confer additional biological activities, e.g., biased signaling. The present review will provide a short overview of the known functionality of chemokines together with the consequences of the interactions engaged by the chemokines with other proteins. Finally, we will present potential therapeutic tools targeting the chemokine multimeric structures that could modulate their biological functions.

Platelets, Protean Cells with All-Around Functions and Multifaceted Pharmacological Applications

Platelets, traditionally known for their roles in hemostasis and coagulation, are the most prevalent blood component after erythrocytes (150,000-400,000 platelets/μL in healthy humans). However, only 10,000 platelets/μL are needed for vessel wall repair and wound healing. Increased knowledge of the platelet's role in hemostasis has led to many advances in understanding that they are crucial mediators in many other physiological processes, such as innate and adaptive immunity. Due to their multiple functions, platelet dysfunction is involved not only in thrombosis, mediating myocardial infarction, stroke, and venous thromboembolism, but also in several other disorders, such as tumors, autoimmune diseases, and neurodegenerative diseases. On the other hand, thanks to their multiple functions, nowadays platelets are therapeutic targets in different pathologies, in addition to atherothrombotic diseases; they can be used as an innovative drug delivery system, and their derivatives, such as platelet lysates and platelet extracellular vesicles (pEVs), can be useful in regenerative medicine and many other fields. The protean role of platelets, from the name of Proteus, a Greek mythological divinity who could take on different shapes or aspects, is precisely the focus of this review.

Methylglyoxal-Modified Human Serum Albumin Binds to Leukocyte Myeloperoxidase and Inhibits its Enzymatic Activity

Hyperglycemia in diabetes mellitus induces modification of proteins by glucose and its derivative methylglyoxal (MG). Neutrophils perform their bactericidal activity mainly via reactive halogen (RHS) and oxygen (ROS) species generation catalyzed by myeloperoxidase (MPO) stored in neutrophil azurophilic granules (AGs) and membrane NADPH oxidase, respectively. Herein, we study the binding of human serum albumin (HSA) modified with MG (HSA-MG) to MPO and its effects on MPO activity and release by neutrophils. Peroxidase activity of MPO was registered by oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, and chlorinating activity by decolorization of Celestine blue B dye. Binding of HSA-MG to MPO was studied by affinity chromatography, disc-electrophoresis, ligand Western blotting and enzyme-linked solid phase immunoassay using monoclonal antibodies (mAbs) to MPO. ROS and RHS generation were detected by lucigenin (Luc) and luminol (Lum) chemiluminescence (CL), respectively. Neutrophil degranulation was assessed by flow cytometry using fluorescent labeled antibodies to the marker proteins CD63 from AGs and CD11b from peroxidase-negative granules (PNGs). NETosis was assayed by quantifying DNA network-like structures (NET-like structures) in blood smears stained by Romanowsky. HSA-MG bound to MPO, giving a stable complex (Kd = 1.5 nM) and competing with mAbs, and non-competitively inhibited peroxidase and chlorinating MPO activity and induced degranulation of PNGs but not of AGs. HSA-MG enhanced Luc-CL per se or following PMA, unlike Lum-CL, and did not affect spontaneous or PMA-stimulated NETosis. Thus, HSA modified under hyperglycemia-like conditions stimulated NADPH oxidase of neutrophils but dampened their functions dependent on activity of MPO, with no effect on its release via degranulation or NETosis. This phenomenon could underlie the downregulation of bactericidal activity of MPO and neutrophils, and hence of innate immunity, giving rise to wound healing impairment and susceptibility to infection in patients with hyperglycemia.

Platelet-leukocyte crosstalk in COVID-19: How might the reciprocal links between thrombotic events and inflammatory state affect treatment strategies and disease prognosis?

Platelet-leukocyte crosstalk is commonly manifested by reciprocal links between thrombosis and inflammation. Platelet thrombus acts as a reactive matrix that recruits leukocytes to the injury site where their massive accumulation, activation and migration promote thrombotic events while triggering inflammatory responses. As a life-threatening condition with the associations between inflammation and thrombosis, COVID-19 presents diffuse alveolar damage due to exaggerated macrophage activity and cytokine storms. These events, together with direct intracellular virus invasion lead to pulmonary vascular endothelialitis, cell membranes disruption, severe endothelial injury, and thrombosis. The developing pre-alveolar thrombus provides a hyper-reactive milieu that recruits circulating leukocytes to the injury site where their activation contributes to thrombus stabilization and thrombosis propagation, primarily through the formation of Neutrophil extracellular trap (NET). NET fragments can also circulate and deposit in further distance where they may disseminate intravascular thrombosis in severe cases of disease. Thrombi may also facilitate leukocytes migration into alveoli where their accumulation and activation exacerbate cytokine storms and tissue damage, further complicating the disease. Based on these mechanisms, whether an effective anti-inflammatory protocol can prevent thrombotic events, or on the other hand; efficient antiplatelet or anticoagulant regimens may be associated with reduced cytokine storms and tissue damage, is now of interests for several ongoing researches. Thus shedding more light on platelet-leukocyte crosstalk, the review presented here discusses the detailed mechanisms by which platelets may contribute to the pathogenesis of COVID-19, especially in severe cases where their interaction with leukocytes can intensify both inflammatory state and thrombosis in a reciprocal manner.

Beyond Hemostasis: Platelet Innate Immune Interactions and Thromboinflammation

There is accumulating evidence that platelets play roles beyond their traditional functions in thrombosis and hemostasis, e.g., in inflammatory processes, infection and cancer, and that they interact, stimulate and regulate cells of the innate immune system such as neutrophils, monocytes and macrophages. In this review, we will focus on platelet activation in hemostatic and inflammatory processes, as well as platelet interactions with neutrophils and monocytes/macrophages. We take a closer look at the contributions of major platelet receptors GPIb, α_IIbβ₃, TLT-1, CLEC-2 and Toll-like receptors (TLRs) as well as secretions from platelet granules on platelet-neutrophil aggregate and neutrophil extracellular trap (NET) formation in atherosclerosis, transfusion-related acute lung injury (TRALI) and COVID-19. Further, we will address platelet-monocyte and macrophage interactions during cancer metastasis, infection, sepsis and platelet clearance.

Circulating extracellular vesicles from patients with valvular heart disease induce neutrophil chemotaxis via FOXO3a and the inhibiting role of dexmedetomidine

We previously demonstrated that circulating extracellular vesicles (EVs) from patients with valvular heart disease (VHD; vEVs) contain inflammatory components and inhibit endothelium-dependent vasodilation. Neutrophil chemotaxis plays a key role in renal dysfunction, and dexmedetomidine (DEX) can reduce renal dysfunction in cardiac surgery. However, the roles of vEVs in neutrophil chemotaxis and effects of DEX on vEVs are unknown. Here, we investigated the impact of vEVs on neutrophil chemotaxis in kidneys and the influence of DEX on vEVs. Circulating EVs were isolated from healthy subjects and patients with VHD. The effects of EVs on chemokine generation, forkhead box protein O3a (FOXO3a) pathway activation and neutrophil chemotaxis on cultured human umbilical vein endothelial cells (HUVECs) and kidneys in mice and the influence of DEX on EVs were detected. vEVs increased FOXO3a expression, decreased phosphorylation of Akt and FOXO3a, promoted FOXO3a nuclear translocation, and activated the FOXO3a signaling pathway in vitro. DEX pretreatment reduced vEV-induced CXCL4 and CCL5 expression and neutrophil chemotaxis in cultured HUVECs via the FOXO3a signaling pathway. vEVs were also found to suppress Akt phosphorylation and activate FOXO3a signaling to increase plasma levels of CXCL4 and CCL5 and neutrophil accumulation in kidney. The overall mechanism was inhibited in vivo with DEX pretreatment. Our data demonstrated that vEVs induced CXCL4-CCL5 to stimulate neutrophil infiltration in kidney, which can be inhibited by DEX via the FOXO3a signaling. Our findings reveal a unique mechanism involving vEVs in inducing neutrophils chemotaxis and may provide a novel basis for using DEX in reducing renal dysfunction in valvular heart surgery.

Luteolin Partially Inhibits LFA-1 Expression in Neutrophils Through the ERK Pathway

Luteolin inhibits the adhesion of neutrophils to microvascular endothelial cells and plays an important anti-inflammatory role, owing to its mechanism of suppressing the expression of lymphocyte function-associated antigen-1 (LFA-1) in the neutrophils. Our study deals with the different signaling pathways participating in LFA-1 expression in neutrophils along with the regulation of luteolin in order to elucidate new anti-inflammatory targets of luteolin, thus providing a basis for clinical applications. In our study, neutrophils were separated using density gradient centrifugation and the cAMP levels were determined using ELISA. Additionally, phosphorylation levels of p38 mitogen-activated protein kinase (MAPK), extracellular regulated protein kinase (ERK), phosphatidylinositol-3-kinase (PI3K), and Janus kinase (JAK) were also detected by Western blotting. LFA-1 expression was estimated using flow cytometry. The results showed that inhibiting agents used against p38 MAPK, ERK, PI3K, and JAK could significantly inhibit LFA-1 expression on neutrophils (p < 0.05, p < 0.01). Luteolin also induced a noteworthy elevation of cAMP in neutrophil supernatants (p < 0.01). It could also significantly inhibit ERK phosphorylation (p < 0.05, p < 0.01), and had no obvious effect on p38 MAPK phosphorylation in neutrophils (p > 0.05). However, phosphorylation of PI3K and JAK was not detected in neutrophils. To conclude, the p38 MAPK, ERK, PI3K, and JAK pathways are involved in the regulation of LFA-1 expression in neutrophils, and luteolin partially inhibits LFA-1 expression by increasing cAMP levels and suppressing ERK phosphorylation.

Start a fire, kill the bug: The role of platelets in inflammation and infection

Platelets are the main players in thrombosis and hemostasis; however they also play important roles during inflammation and infection. Through their surface receptors, platelets can directly interact with pathogens and immune cells. Platelets form complexes with neutrophils to modulate their capacities to produce reactive oxygen species or form neutrophil extracellular traps. Furthermore, they release microbicidal factors and cytokines that kill pathogens and influence the immune response, respectively. Platelets also maintain the vascular integrity during inflammation by a mechanism that is different from classical platelet activation. In this review we summarize the current knowledge about how platelets interact with the innate immune system during inflammation and infection and highlight recent advances in the field.

Neutrophil Adhesion Is a Prerequisite for Antibody-Mediated Proteolytic Tissue Damage in Experimental Models of Epidermolysis Bullosa Acquisita

Although uncontrolled proteolytic activity mediated by activated neutrophils is a major reason for tissue damage, therapeutic approaches using protease inhibitors are inefficient. Here, we investigated the role of the immune complex-induced neutrophil adhesion and protease release in tissue damage. We show both in vitro and in vivo that immune complex-mediated neutrophil adhesion to the target tissue depends on β₂ integrins. Without affecting elastase or reactive oxygen species release, blocking of adhesion drastically inhibited tissue damage in an experimental model of autoantibody-mediated skin blistering disease. By using a cell-bound fluorescent resonance energy transfer-based elastase sensor, we detected elastase enzyme activity on the surface of adherent cells resistant to protease inhibitors. Inhibitor resistance was lost by CD18 blockade or deficiency in vitro and in vivo. Immune complex-induced neutrophil adhesion created an enclosed protected space between the cell and its target structure where proteinases and reactive oxygen species can execute their tissue-damaging effect. Because immune complex-induced neutrophil adhesion represents an indispensable step for tissue damage of many diseases, our findings may facilitate the development of strategies for the treatment of such disorders.

CXCL4-induced macrophages in human atherosclerosis

Atherosclerosis is considered an inflammatory disease of the arterial wall. Monocytes and monocyte-derived cells (most often termed macrophages) play an essential role in the formation of atherosclerotic lesions, as they take up lipids leading to subsequent foam cell formation accompanied by release of pro-inflammatory cytokines. Similarly, platelets have been discovered to represent an important cell type mediating inflammatory and immune processes in atherogenesis, mainly by secreting chemokines, which are stored in the platelets' alpha granules, upon platelet activation. Therefore, the interaction between monocyte-derived cells and platelets is of exceptional importance. In this review, we specifically focus on the chemokine (platelet factor-4, PF4) and its effects on monocytes and monocyte-derived cells. By formation of heterodimers dimers and -oligomers with CCL5, CXCL4 induces binding of monocytes cells to endothelial cell and thereby promotes diapedesis of monocytes into the subendothelial space. CXCL4 also affects the differentiation of monocytes as it induces a specific macrophage phenotype, which we suggested to term "M4". For example, CXCL4-induced macrophages irreversibly lose the hemoglobin-haptoglobin scavenger receptor CD163. The combination of CD68, S100A8, and MMP7 turned out to reliably identify M4 macrophages both in vitro and in vivo within atherosclerotic lesions. In human atherosclerotic plaques, M4 macrophages are predominantly present in the adventitia and the intima and their prevalence is associated with plaque instability suggesting that they are a marker of pro-inflammatory activity. Overall, CXCL4-induced M4 macrophages may represent a target for diagnostic and therapeutic interventions in human atherosclerotic disease.

Chemokine CXCL7 Heterodimers: Structural Insights, CXCR2 Receptor Function, and Glycosaminoglycan Interactions

Chemokines mediate diverse fundamental biological processes, including combating infection. Multiple chemokines are expressed at the site of infection; thus chemokine synergy by heterodimer formation may play a role in determining function. Chemokine function involves interactions with G-protein-coupled receptors and sulfated glycosaminoglycans (GAG). However, very little is known regarding heterodimer structural features and receptor and GAG interactions. Solution nuclear magnetic resonance (NMR) and molecular dynamics characterization of platelet-derived chemokine CXCL7 heterodimerization with chemokines CXCL1, CXCL4, and CXCL8 indicated that packing interactions promote CXCL7-CXCL1 and CXCL7-CXCL4 heterodimers, and electrostatic repulsive interactions disfavor the CXCL7-CXCL8 heterodimer. As characterizing the native heterodimer is challenging due to interference from monomers and homodimers, we engineered a “trapped” disulfide-linked CXCL7-CXCL1 heterodimer. NMR and modeling studies indicated that GAG heparin binding to the heterodimer is distinctly different from the CXCL7 monomer and that the GAG-bound heterodimer is unlikely to bind the receptor. Interestingly, the trapped heterodimer was highly active in a Ca²⁺ release assay. These data collectively suggest that GAG interactions play a prominent role in determining heterodimer function in vivo. Further, this study provides proof-of-concept that the disulfide trapping strategy can serve as a valuable tool for characterizing the structural and functional features of a chemokine heterodimer.

Platelet secretion in inflammatory and infectious diseases

Platelets are small, anucleate circulating cells that possess a dynamic repertoire of functions spanning the hemostatic, inflammatory, and immune continuum. Once thought to be merely cell fragments with responses limited primarily to acute hemostasis and vascular wall repair, platelets are now increasingly recognized as key sentinels and effector cells regulating host responses to many inflammatory and infectious cues. Platelet granules, including α-granules and dense-granules, store hundreds of factors and secrete these mediators in response to activating signals. The cargo packaged and stored within platelet granules orchestrates communication between platelets and other circulating cells, augments host defense mechanisms to invading pathogens and tumor cells, and - in some settings - drives dysregulated and injurious responses. This focused review will highlight several of the established and emerging mechanisms and roles of platelet secretion in inflammatory and infectious diseases.

Platelets: New Bricks in the Building of Neutrophil Extracellular Traps

In addition to being key elements in hemostasis and thrombosis, platelets have an important role in the inflammatory and innate immune response. This activity is associated with their capability to recognize pathogens through the expression of toll-like receptors, the secretion of various cytokines, chemokines, and growth factors stored within their granules, and the expression of cell adhesion molecules that allows interaction with other immune cells, mainly neutrophils and monocytes. As part of the first line of defense, neutrophils control invading pathogens by phagocytosis, the release of antimicrobial proteins during degranulation, or through the formation of web-like structures named neutrophil extracellular traps (NETs). NETs are formed by chromatin, proteases, and antimicrobial proteins, and their main function is to trap and kill bacteria, virus, and fungi, avoiding their dissemination. Besides microorganisms, NET formation is also triggered by proinflammatory molecules and platelets. The uncontrolled formation of NETs might exert tissue damage and has been involved in a pathogenic mechanism of autoimmune and prothrombotic clinical conditions. In this review, we discuss the role of platelets in NET generation highlighting the mediators, stimuli, and molecular mechanisms involved in this phenomenon, both in human and murine models.

Local translation of TC10 is required for membrane expansion during axon outgrowth

The surface of developing axons expands in a process mediated by the exocyst complex. The spatial-temporal regulation of the exocyst is only partially understood. Here we report that stimulated membrane enlargement in dorsal root ganglion (DRG) axons is triggered by intra-axonal synthesis of TC10, a small GTPase required for exocyst function. Induced membrane expansion and axon outgrowth are inhibited after axon-specific knockdown of TC10 mRNA. To determine the relationship of intra-axonal TC10 synthesis with the previously described stimulus-induced translation of the cytoskeletal regulator Par3, we investigate the signaling pathways controlling their local translation in response to NGF. Phosphoinositide 3-kinase (PI3K)-dependent activation of the Rheb-mTOR pathway triggers the simultaneous local synthesis of TC10 and Par3. These results reveal the importance of local translation in the control of membrane dynamics and demonstrate that localized, mTOR-dependent protein synthesis triggers the simultaneous activation of parallel pathways.

EndoS reduces the pathogenicity of anti-mCOL7 IgG through reduced binding of immune complexes to neutrophils

Endo-β-N-acetylglucosaminidase (EndoS) has been shown to act as a potent pathogen-derived immunomodulatory molecule in autoimmune diseases. Here we investigated how EndoS treatment reduces the pathogenicity of rabbit anti-mCOL7 IgG using different experimental models of epidermolysis bullosa acquisita (EBA). Our results show that the EndoS treatment does not interfere with the binding of the antibody to the antigen but reduces immune complex (IC)-mediated neutrophil activation by impairing the binding of the IC to FcγR on neutrophils. On the basis of this newly identified EndoS-mediated mechanism we hope to develop new strategies in the treatment of the disease.

Off-pump coronary artery bypass surgery induces prolonged alterations to host neutrophil physiology

Persistent alteration to host polymorphonuclear cell (PMN) physiology has been demonstrated after cardiac surgery performed with cardiopulmonary bypass (CPB). However, to date, PMN physiology and function beyond the first 24 h have not been investigated after cardiac surgery performed without CPB (off-pump coronary artery bypass grafting [OPCAB]). Blood samples of 15 patients were collected preoperatively and on days 1, 3, and 5 after OPCAB. Expression of CD11b, CD18, CBRM1/5, and CD62L were assessed by flow cytometry under resting conditions and after stimulation with formyl methionyl-leucyl-phenylalanine (fMLF), and respiratory burst activity was also measured. Under resting conditions, PMN CD11b, CBRM1/5, and CD62L expressions were minimally altered by surgery. Compared with the response of preoperative PMNs, PMNs assayed on days 3 and 5 after OPCAB demonstrated a significantly blunted increase in the expression of CD11b and CBRM1/5 after fMLF, significantly diminished shedding of CD62L in response to platelet-activating factor and fMLF, and diminished superoxide production after stimulation on day 3. The alteration of PMN function after OPCAB implies that cardiac surgical trauma without CPB directly modulates host PMN physiology.

Quantitative pattern analysis of the N-terminally processed isoforms of platelet factor-4 in serum

RATIONALE

Platelet factor 4 (PF4) is a small cytokine belonging to the CXC chemokine family which has been shown to play a role in inflammation and in the regulation of angiogenesis. In general, chemokines are susceptible to proteolytic cleavage in amino and carboxy terminal regions, which usually results in dramatic changes to the chemokine bioactivity. The purpose of this study was to identify various platelet factor-4 (PF4) isoforms caused by proteolytic processing and to quantify their levels in normal serum.

METHODS

First, we identified the N-terminally truncated PF4 isoforms from a standard purified PF4 protein sample by using mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analysis. Then, we used high-performance liquid chromatography (HPLC) to semi-purify PF4 from serum samples, and the levels of the four most abundant PF4 isoforms were quantitatively determined using selected reaction monitoring (SRM) assays on a nano-LC/triple-quadrupole mass spectrometer.

RESULTS

We have identified seven N-terminally processed PF4 isoforms and compared the levels of major PF4 isoforms from nine serum samples. Pro-p1 (EAEEDGDLQCLCVK-; average MW, 7765.2) is the major PF4 isoform in serum whereas the PF4 isoforms, designated Prot-p4 (FASAEAEEDGDLQCLCVK-;average MW, 8141.5), Prot-p3 (SAEAEEDGDLQCLCVK-; average MW, 7923.3), and Prot-p2 (AEEDGDLQCLCVK- ; average MW, 7836.3), are at about 16%, 3%, and 2% levels of the major one, respectively.

CONCLUSIONS

This study is the first report on the levels of N-terminally processed PF4 isoforms in serum. Also, this study shows the usefulness of SRM in determining concentrations of protein isoform variants, which can be often overlooked in immunoassay analysis.

Platelets in atherosclerosis and thrombosis

Rupture of an atherosclerotic plaque exposes a thrombogenic matrix, which instantly triggers platelet tethering and activation. We here delineate the sequence of events during arterial thrombus formation and dissect the specific role of the various platelet receptors in this process. We also discuss the interplay of platelets with circulating immune cells, which support arterial thrombosis by fibrin formation in a process that involves extracellular nucleosomes. In the second part of this chapter we describe the role of platelets in atherosclerotic lesion formation. Platelets adhere to the dysfunctional endothelium early during atherogenesis. They contain a large machinery of proinflammatory molecules, which can be released upon their activation. This prepares the ground for subsequent leukocyte recruitment and infiltration, and boosts the inflammatory process of the arterial wall. Together, platelets play a critical role in both acute and chronic processes of the vascular wall, which makes them an attractive target for pharmacological strategies to treat arterial thrombosis and, potentially, also atheroprogression.

Ginkgolide B reduces atherogenesis and vascular inflammation in ApoE(-/-) mice

Aims

To investigate whether ginkgolide B (a platelet-activating factor inhibitor) affects vascular inflammation in atherosclerosis-prone apolipoprotein E-deficient (ApoE^−/−) mice.

Methods and Results

Human platelets were used to evaluate the effects of ginkgolide B on platelet aggregation and signal transduction. Ginkgolide B attenuated platelet aggregation and inhibited phosphatidylinositol 3 kinase (PI3K) activation and Akt phosphorylation in thrombin- and collagen-activated platelets. ApoE^−/− mice were administered a high-cholesterol diet for 8 weeks. Plasma platelet factor 4 (PF4) and RANTES (regulated upon activation, normal T-cell expressed, and secreted protein) were then measured using an enzyme-linked immunosorbent assay. Scanning electron microscopy and immunohistochemistry were used to determine atherosclerotic lesions. Ginkgolide B decreased plasma PF4 and RANTES levels in ApoE^−/− mice. Scanning electron microscopic examination showed that ginkgolide B reduced aortic plaque in ApoE^−/− mice. Immunohistochemistry analysis demonstrated that ginkgolide B diminished P-selectin, PF4, RANTES, and CD40L expression in aortic plaque in ApoE^−/− mice. Moreover, ginkgolide B suppressed macrophage and vascular cell adhesion protein 1 (VCAM-1) expression in aorta lesions in ApoE^−/− mice. Similar effects were observed in aspirin-treated ApoE^−/− mice.

Conclusion

Ginkgolide B significantly reduced atherosclerotic lesions and P-selectin, PF4, RANTES, and CD40L expression in aortic plaque in ApoE−/− mice. The efficacy of ginkgolide B was similar to aspirin. These results provide direct evidence that ginkgolide B inhibits atherosclerosis, which may be associated with inhibition of the PI3K/Akt pathway in activated platelets.

Platelets in atherosclerosis

Beyond obvious functions in haemostasis and thrombosis, platelets are considered to be essential in proinflammatory surroundings such as atherosclerosis, allergy, rheumatoid arthritis and even cancer. In atherosclerosis, platelets facilitate the recruitment of inflammatory cells towards the lesion sites and release a plethora of inflammatory mediators, thereby enriching and boosting the inflammatory milieu. Platelets do so by interacting with endothelial cells, circulating leukocytes (monocytes, neutrophils, dendritic cells, T-cells) and progenitor cells. This cross-talk enforces leukocyte activation, adhesion and transmigration. Furthermore, platelets are known to function in innate host defense through the release of antimicrobial peptides and the expression of pattern recognition receptors. In severe sepsis, platelets are able to trigger the formation of neutrophil extracellular traps (NETs), which bind and clear pathogens. The present antiplatelet therapies that target key pathways of platelet activation and aggregation therefore hold the potential to modulate platelet-derived immune functions by reducing cellular interactions of platelets with other immune components and by reducing the secretion of inflammatory proteins into the milieu. The objective of this review is to update and discuss the current perceptions of the platelet immune constituents and their prospect as therapeutic targets in an atherosclerotic setting.

Molecular pathways of platelet factor 4/CXCL4 signaling

The platelet-derived chemokine CXCL4 takes a specific and unique position within the family of chemotactic cytokines. Today, much attention is directed to CXCL4's capacity to inhibit angiogenesis and to promote innate immune responses, which makes this chemokine an interesting tool and target for potential intervention in tumor growth and inflammation. However, such attempts demand a comprehensive knowledge on the molecular mechanisms and pathways underlying the corresponding cellular functions. At least two structurally different receptors, CXCR3-B and a chondroitin sulfate proteoglycan, are capable of binding CXCL4 and to induce a specific intracellular signaling machinery. While signaling mediated by CXCR3-B involves Gs proteins, elevated cAMP levels, and p38 MAP kinase, signaling via proteoglycans appears to be more complicated and varies strongly between the cell types analyzed. In CXCL4-activated neutrophils and monocytes, tyrosine kinases of the Src family and Syk as well as monomeric GTPases and members of the MAP kinase family have been identified as essential intracellular signals. Most intriguingly, signaling does not proceed in a linear sequence of events but in a repeated activation of certain transducing elements like Rac2 or sphingosine kinase 1. Depending on the downstream targets, such biphasic kinetics either leads to a redundant and prolonged activation of a single pathway or to a timely separated initiation of disparate signals and functions. Results of the studies reviewed here help to understand the molecular basis of CXCL4's functional diversity and provide insights into integrated signaling processes in general.

The role of the CXC chemokines platelet factor-4 (CXCL4/PF-4) and its variant (CXCL4L1/PF-4var) in inflammation, angiogenesis and cancer

Chemokines are chemotactic cytokines which recruit leukocytes to inflammatory sites. They also affect tumor development and metastasis by acting as growth factor, by attracting pro- or anti-tumoral leukocytes or by influencing angiogenesis. Platelet factor-4 (CXCL4/PF-4) was the first chemokine shown to inhibit angiogenesis. CXCL4L1/PF-4var, recently isolated from thrombin-stimulated platelets, differing from authentic CXCL4/PF-4 in three carboxy-terminally located amino acids, was found to be more potent than CXCL4/PF-4 in inhibiting angiogenesis and tumor growth. Both glycosaminoglycans (GAG) and CXCR3 are implicated in the activities of the PF-4 variants. This report reviews the current knowledge on the role of CXCL4/PF-4 and CXCL4L1/PF-4var in physiological and pathological processes. In particular, the role of CXCL4/PF-4 in cancer, heparin-induced thrombocytopenia and atherosclerosis is described.

Platelet-derived chemokines: pathophysiology and therapeutic aspects

The identification of chemokines in blood platelets has strengthened our view of these cells as participants in immune host defense. Platelet chemokines representing prestored and rapidly releasable proteins may play a major role as first-line inflammatory mediators. This is evident from their capability to recruit early inflammatory cells such as neutrophil granulocytes and monocytes and even to exhibit direct antimicrobial activity. However, insight is growing that platelet chemokines may be also long-term regulators, e.g., by activating T lymphocytes, by modulating the formation of endothelium and even thrombocytopoiesis itself. This review deals with the individual and cooperative functionality of platelet chemokines, as well as their potential as a basis for therapeutic intervention in the pathology of inflammation, infection, allergy and tumors. Within this context, therapeutic strategies based on the use of antibodies, modified chemokines, chemokine-binding proteins and chemokine receptor antagonists as well as first clinical studies will be addressed.

Platelets control leukocyte recruitment in a murine model of cutaneous arthus reaction

Platelets have been shown to be important in inflammation, but their role in the cutaneous Arthus reaction remains unclear. To assess the role of platelets in this pathogenetic process, the cutaneous Arthus reaction was examined in wild-type mice and mice lacking E-selectin, P-selectin, or P-selectin glycoprotein ligand-1 (PSGL-1) with or without platelet depletion by busulfan, a bone marrow precursor cell-specific toxin. Edema and hemorrhage induced by immune complex challenge significantly decreased in busulfan-treated wild-type mice compared with untreated mice. Busulfan treatment did not affect edema and hemorrhage in P-selectin- or PSGL-1-deficient mice, suggesting that the effect by busulfan is dependent on P-selectin and PSGL-1 expression. The inhibited edema and hemorrhage paralleled reduced infiltration of neutrophils and mast cells and reduced levels of circulating platelets. Increased cutaneous production of interleukin-6, tumor necrosis factor-alpha, and platelet-derived chemokines during Arthus reaction was inhibited in busulfan-treated wild-type mice relative to untreated mice, which paralleled the reduction in cutaneous inflammation. Flow cytometric analysis showed that immune complex challenge generated blood platelet-leukocyte aggregates that decreased by busulfan treatment. In thrombocytopenic mice, the cutaneous inflammation after immune complex challenge was restored by platelet infusion. These results suggest that platelets induce leukocyte recruitment into skin by forming platelet-leukocyte aggregates and secreting chemokines at inflamed sites, mainly through the interaction of P-selectin on platelets with PSGL-1 on leukocytes.

Platelet factor 4 is highly upregulated in dendritic cells after severe trauma

Dendritic cells (DCs) represent an important linkage between the innate and adaptive immune system and express proinflammatory transcriptomic products early after trauma. The use of a genomic approach recently revealed that platelet factor 4 (PF4) is significantly upregulated in DCs in patients after multiple trauma. However, knowledge about subsequent PF4 alteration and its potential clinical relevance in the context of multiple trauma is still limited. We used quantitative reverse transcription-polymerase chain reaction to analyze PF4 expression in both myeloid DCs (MDCs) and plasmocytoid DCs (PDCs) isolated from 10 patients after multiple trauma. Intracellular PF4 as well as HLA-DR expression were detected by flow cytometry. Furthermore, DCs and peripheral blood mononuclear cells were incubated on a monolayer of human umbilical endothelial cells and their adhesion properties were analyzed. The ratio of the DC subtypes (MDC and PDC) was assessed by flow cytometry. PF4 expression significantly increased on d 1 and d 2 as measured by reverse transcription-polymerase chain reaction. Intracellular PF4 content in MDCs and PDCs was significantly elevated in trauma patients compared with healthy controls. In addition, the surface antigen HLA-DR on MDCs was significantly elevated on d 1 and d 4 after trauma in patients compared with controls. However, cell adhesion of DCs did not show any significant differences between patients and controls. PF4 concentration in MDCs and PDCs significantly correlated with the injury severity score. These results confirm an early and subsequent posttraumatic activation of PF4 in DCs. PF4 also participates in the posttraumatic activation of DCs in relation to injury severity, a role that might be preferably based on the modification of receptor expression, whereas adhesion properties are largely unaffected.

Platelet alpha-granules: basic biology and clinical correlates

alpha-Granules are essential to normal platelet activity. These unusual secretory granules derive their cargo from both regulated secretory and endocytotic pathways in megakaryocytes. Rare, inheritable defects of alpha-granule formation in mice and man have enabled identification of proteins that mediate cargo trafficking and alpha-granule formation. In platelets, alpha-granules fuse with the plasma membrane upon activation, releasing their cargo and increasing platelet surface area. The mechanisms that control alpha-granule membrane fusion have begun to be elucidated at the molecular level. SNAREs and SNARE accessory proteins that control alpha-granule secretion have been identified. Proteomic studies demonstrate that hundreds of bioactive proteins are released from alpha-granules. This breadth of proteins implies a versatile functionality. While initially known primarily for their participation in thrombosis and hemostasis, the role of alpha-granules in inflammation, atherosclerosis, antimicrobial host defense, wound healing, angiogenesis, and malignancy has become increasingly appreciated as the function of platelets in the pathophysiology of these processes has been defined. This review will consider the formation, release, and physiologic roles of alpha-granules with special emphasis on work performed over the last decade.

Platelet chemokines in vascular disease

Platelets are a rich source of different chemokines and express chemokine receptors. CXCL4 is highly abundant in platelets and involved in promoting monocyte arrest from rolling and monocyte differentiation to macrophages. CXCL4 can also associate with CCL5 and amplify its effect on monocytes. The megakaryocyte CXCL7 gene product is proteolytically cleaved into the strong neutrophil chemoattractant, NAP-2, which has also been implicated in repair cell homing to vascular lesions. Platelet adhesion can induce release of CCL2 and CXCL8 from endothelial cells. Conversely, the chemokines CCL17, CCL22, and CXCL12 made by other cells amplify platelet activation. Platelet chemokines enhance recruitment of various hematopoietic cells to the vascular wall, fostering processes such as neointima formation, atherosclerosis, and thrombosis, but also vessel repair and regeneration after vascular injury.

Apolipoprotein A-I and platelet factor 4 are biomarkers for infliximab response in rheumatoid arthritis

OBJECTIVES

The use of biologicals such as infliximab has dramatically improved the treatment of rheumatoid arthritis (RA). However, factors predictive of therapeutic response need to be identified. A proteomic study was performed prior to infliximab therapy to identify a panel of candidate protein biomarkers of RA predictive of treatment response.

METHODS

Plasma profiles of 60 patients with RA (28 non-responders (as defined by the American College of Rheumatology 20% improvement criteria (ACR20)) negative and 32 responders (ACR70 positive) to infliximab) were studied by surface enhanced laser desorption/ionisation time-of-flight mass spectrometry (SELDI-TOF MS) technology on two types of arrays, an anion exchange array (SAX2) and a nickel affinity array (IMAC3-Ni). Biomarker characterisation was carried out using classical biochemical methods (purification by ammonium sulfate precipitation or metal affinity chromatography) and identification by matrix assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS analysis.

RESULTS

Two distinct protein profiles were observed on both arrays and several proteins were differentially expressed in both patient populations. Five proteins at 3.86, 7.77, 7.97, 8.14 and 74.07 kDa were overexpressed in the non-responder group, whereas one at 28 kDa was increased in the responder population (sensitivity>56%, specificity>77.5%). Moreover, combination of several biomarkers improved the sensitivity and specificity of the detection of patient response to over 97%. The 28 kDa protein was characterised as apolipoprotein A-I and the 7.77 kDa biomarker was identified as platelet factor 4.

CONCLUSIONS

Six plasma biomarkers are characterised, enabling the detection of patient response to infliximab with high sensitivity and specificity. Apolipoprotein A-1 was predictive of a good response to infliximab, whereas platelet factor 4 was associated with non-responders.

Activation of p38(MAPK) mediates the angiostatic effect of the chemokine receptor CXCR3-B

Chemokines binding the CXCR3 receptor have been shown to inhibit angiogenesis via the CXCR3-B isoform, but the underlying molecular mechanisms are unknown. Aim of this study was to elucidate the effects of CXCR3-B on activation of members of the mitogen-activated protein kinase family, and to explore the relevance of defined signaling pathways to the angiostatic effects of CXCR3-B ligands. Human embryonic kidney (HEK) 293 cells were transfected with expression vectors encoding for CXCR3-A or CXCR3-B. In cells expressing CXCR3-A, CXCL10 (IP-10) at nanomolar concentrations induced activation of ERK, Akt, and Src, as previously described in human vascular pericytes. In HEK-293 cells expressing CXCR3-B, exposure to CXCL10 in the micromolar concentration range led to activation of the p38(MAPK) pathway, as indicated by phosphorylation of p38(MAPK) itself, and of MKK3/6 and MAPKAPK-2, that lie upstream and downstream of p38(MAPK), respectively. Similar results were obtained in cells stimulated with CXCL4 (PF4), a specific ligand of CXCR3-B. In contrast, CXCL4 was unable to activate p38(MAPK) in mock-transfected HEK-293 cells. Only a modest induction of ERK or JNK was observed upon CXCR3-B activation. In human microvascular endothelial cells, which selectively express CXCR3-B, in a cell cycle-dependent fashion, CXCL10 and CXCL4 increased the enzymatic activity of p38(MAPK). Pharmacologic inhibition of p38(MAPK) by SB302580 resulted in a significant increase in DNA synthesis and in reversal of the inhibitory action of CXCL10. In conclusion, the p38(MAPK) pathway is a downstream effector of CXCR3-B implicated in the angiostatic action of this chemokine receptor.

Platelet factor-4 is an indicator of blood count recovery in acute myeloid leukemia patients in complete remission

To investigate whether serum biomarkers can be used to indicate the responsiveness of acute myeloid leukemia to remission induction chemotherapy, we performed MALDI-TOF protein profile analysis of patient sera. The resulting spectra revealed a protein (or peptide) peak at m/z 7764 that varied in intensity; its intensity was much higher in samples from patients in complete remission than in those from patients with resistant disease or in samples taken prior to treatment (at the time of diagnosis). Using fractionation, trypsin digestion, MS/MS, and protein molecular weight analyses, we identified the m/z 7764 protein as platelet factor-4 (PF4). This identification was confirmed by a magnetic bead-based MALDI immunoassay. Statistical comparison of PF4 levels and platelet counts in patient sera revealed a significant positive correlation between the two variables. This study demonstrates that PF4 protein levels are a good indicator for the recovery of blood count in the complete remission of acute myeloid leukemia. The linear positive correlation curve indicates that blood count recovery of platelets to >100,000/mm(3) is equivalent to a serum PF4 recovery level of >2.492 microg/ml.

CXCR1/2 ligands induce p38 MAPK-dependent translocation and release of opioid peptides from primary granules in vitro and in vivo

Polymorphonuclear leukocytes (PMN) can release opioid peptides which bind to opioid receptors on sensory neurons and inhibit inflammatory pain. This release can be triggered by chemokine receptor 1/2 (CXCR1/2) ligands. Our aim was to identify the granule subpopulation containing opioid peptides and to assess whether MAPK mediate the CXCR1/2 ligand-induced release of these peptides. Using double immunofluorescence confocal microscopy, we showed that beta-endorphin (END) and Met-enkephalin (ENK) were colocalized with the primary (azurophil) granule markers CD63 and myeloperoxidase (MPO) within PMN. END and ENK release triggered by a CXCR1/2 ligand in vitro was dependent on the presence of cytochalasin B (CyB) and on p38 MAPK, but not on p42/44 MAPK. In addition, translocation of END and ENK containing primary granules to submembranous regions of the cell was abolished by the p38 MAPK inhibitor SB203580. In vivo CXCL2/3 reduced pain in rats with complete Freund's adjuvant (CFA)-induced hindpaw inflammation. This effect was attenuated by intraplantar (i.pl.) antibodies against END and ENK and by i.pl. p38 MAPK inhibitor treatment. Taken together, these findings indicate that END and ENK are contained in primary granules of PMN, and that CXCR1/2 ligands induce p38-dependent translocation and release of these opioid peptides to inhibit inflammatory pain.

Platelet factor 4 (CXC chemokine ligand 4) differentially regulates respiratory burst, survival, and cytokine expression of human monocytes by using distinct signaling pathways

Platelet factor 4 (PF4; CXCL4) is an abundant platelet alpha-granule CXC chemokine with unique functions. Although lacking a chemotactic activity, PF4 initiates a signal transduction cascade in human monocytes leading to the induction of a broad spectrum of acute and delayed functions including phagocytosis, respiratory burst, survival, and the secretion of cytokines. Surprisingly, although these monocyte functions are well defined, only very limited information exists on the specific signaling pathways that are involved in the regulation of these biological responses. By using specific inhibitors and direct phosphorylation/activation studies, we show in the present study that PF4-mediated respiratory burst is dependent on a very rapid activation of PI3K, Syk, and p38 MAPK. Moreover, monocyte survival and differentiation instead is controlled by a delayed activation of Erk, with an activity peak after 6 h of stimulation. The inhibition of Erk completely reverted PF4-mediated protection against apoptosis. Finally, even though JNK is rapidly activated in PF4-treated monocytes, it is dispensable for the regulation of survival and respiratory burst. However, PF4-induced up-regulation of chemokine and cytokine mRNA and protein requires a sustained activation of JNK and Erk. Taken together, PF4-stimulated immediate monocyte functions (oxygen radical formation) are regulated by p38 MAPK, Syk, and PI3K, whereas delayed functions (survival and cytokine expression) are controlled by Erk and JNK.

Platelets as immune cells: bridging inflammation and cardiovascular disease

Beyond an eminent role in hemostasis and thrombosis, platelets are characterized by expert functions in assisting and modulating inflammatory reactions and immune responses. This is achieved by the regulated expression of adhesive and immune receptors on the platelet surface and by the release of a multitude of secretory products including inflammatory mediators and cytokines, which can mediate the interaction with leukocytes and enhance their recruitment. In addition, platelets are characterized by an enormous surface area and open canalicular system, which in concert with specialized recognition receptors may contribute to the engulfment of serum components, antigens, and pathogens. Platelet-dependent increases in leukocyte adhesion may not only account for an exacerbation of atherosclerosis, for arterial repair processes, but also for lymphocyte trafficking during adaptive immunity and host defense. This review compiles a selection of platelet-derived tools for bridging inflammation and vascular disease and highlights the molecular key components governing platelet-mediated mechanisms operative in immune surveillance, vascular remodeling, and atherosclerosis.

Neutrophil adhesion to endothelial cells induced by platelet factor 4 requires sequential activation of Ras, Syk, and JNK MAP kinases

Signal transduction mechanisms associated with neutrophil activation by platelet factor 4 (PF4; CXCL4) are as yet poorly characterized. In a recent report, we showed that PF4-induced neutrophil functions (such as adhesion and secondary granule exocytosis) involve the activation of Src-kinases. By analyzing intracellular signals leading to adherence, we here demonstrate by several lines of evidence that in addition to Src-kinases, PF4 signaling involves the monomeric GTPase Ras, the tyrosine kinase Syk, and the MAP kinase JNK. Furthermore, on stimulation, GTPases Rac2 and RhoA were activated, and each was translocated to a different membrane compartment. As shown by inhibitor studies, Rac2 and JNK are located downstream of Syk and Ras. Most intriguingly, the latter 2 elements appear to control the activity of Rac2 and JNK independently of each other at different phases of the activation process. Although a first phase of Rac2 and JNK activation of up to 5 minutes is initiated by Ras, the second phase (5-30 minutes) depends predominantly on the activity of Syk. In summary, we describe that coordinated activity of Syk, Ras, and JNK mediates neutrophil adhesion to endothelial cells and that PF4 induces sequential activation of these elements.

Differential and additive effects of platelet-derived chemokines on monocyte arrest on inflamed endothelium under flow conditions

Platelet-derived chemokines, such as regulated on activation, normal T expressed and secreted (RANTES; CC chemokine ligand 5), platelet factor 4 [PF4; CXC chemokine ligand 4 (CXCL4)], and epithelial neutrophil-activating protein 78 (ENA-78; CXCL5), or precursors, such as beta-thromboglobulin, which can be processed to neutrophil-activating protein-2 (NAP-2; CXCL7), may play an important role in monocyte recruitment during atherogenesis. Platelets can deposit chemokines on inflamed endothelium; however, little is known about differential or additive effects of platelet chemokines on monocyte arrest. Here, we demonstrate that preincubation of activated human microvascular endothelial cells (HMVECs) with RANTES, PF4, or NAP-2 but not ENA-78 dose-dependently increased surface immobilization and subsequent monocyte arrest in flow. RANTES was the most potent and efficient arrest chemokine. Pretreatment of HMVECs with beta-thromboglobulin enhanced monocyte arrest in the presence of cathepsin G generating NAP-2. Combined pretreatment of HMVECs with RANTES and PF4 at suboptimal concentrations synergistically increased arrest, and preincubation with chondroitinase ABC abrogated RANTES- and PF4-induced monocyte arrest. This was associated with reduced expression of chondroitin sulfate, RANTES, and PF4 on the HMVEC surface. Perfusion of HMVECs with platelets known to deposit RANTES and PF4 on the endothelial surface enhanced monocyte arrest, which was inhibited by Met-RANTES, chondroitinase, or a blocking antibody to PF4 but not to ENA-78. The relevance of platelet-derived chemokines was confirmed in adhesion assays with activated whole blood, where Met-RANTES and to a lesser extent, antibodies to PF4 and NAP-2 inhibited arrest of CD14-positive monocytes. Thus, multiple platelet-derived chemokines and processable precursors, which can be presented by specific endothelial proteoglycans, may contribute and cooperate differentially to induce monocyte recruitment.

Gene expression profiles of peripheral and cord blood mononuclear cells altered by thymic stromal lymphopoietin

Thymic stromal lymphopoietin (TSLP) was reported to induce dendritic cells to produce Th2-attracting chemokines, followed by allergic inflammation through stimulating not only CD4-positive T cells but also CD8-positive T cells. Therefore, in this experiment, GeneChip and hierarchical clustering were applied to screen the molecules in whole immunity triggered by TSLP directly and indirectly using both adult peripheral and cord blood mononuclear cells as well as isolated monocytes. Gene expression profiles screened a variety of molecules that are triggered by TSLP with or without CD40 ligation. In the profile, RNA expressions of indoleamine 2,3-dioxygenase, that is known to induce anergy of T cells and natural killer cells in protecting fetal rejection; many kinds of proteasomes that were reported to trigger cytokine production by inhibiting suppressors of NF-kappaB; and several kinds of chemokines increased, whereas RNA expression of superoxide dismutase 1 decreased, which was unexpected but considered worthy of notice. Expression of chemokines at protein levels and enzymatic activity of indoleamine 2,3-dioxygenase was further confirmed to increase in the presence of TSLP using ELISA and HPLC, respectively. These results suggest that the advent of microarray technology may enable us to screen novel molecular targets to treat TSLP-related allergic inflammation.